Brush



Feb. 17, 1942. G. E. MILLARD ETAL 2,273,717

BRUSH Filed Jan. 14-, '193 s Sheets-Sheet 1 INVNTOR5 GLEN E-MILLARDWILLIAM G. HUGHES ATTORNEYS Feb. 17,1942. G. E. MILLARD am y 2,273,717

BRUSH Filed Jan. 14, 1938 3 Sheets-She et 2 7 INVENTOR$ GLEN E. MILLARDWILLIAM G. HueHEs ATTORN 5Y5 Patented Feb. 17, 1942 r jBRUSHY"GlenE'iMillardlalid WilliamG. HughesQSt. Paul,

Minnl, "assignorsfto Lactona Incorporated, St., l A

F Paul, Minn, a corporation of Minnesota Application january 14, 1938,Serial No. 184,982

s'ciaims. 01115-167) This invention relates to improvementsin brushconstruction by which 'the'servicelife of the bristles of the brush maybe lengthened; Bristles of brushes'are subject to fatigue failurewhe'nrepeatedly flexed beyond the endurance limit of the bristle material,with resultant shortening of the service life of the brush. This isparticularly true of large diameter bristles,\"of brushes. containingbristles of various diameters because in the larger diameter bristlesthe stress within the'material may be increased beyond the endurancelimit. It is also particularly true of bristles along the outside row ofa brush because thesebristles are usually flexedto a greater extent thanthe average deflection of the brush. Although some grading of bristlesis possible, most brusheshave bristles of varyingdiameters and thecondition of breakage of large size bristles andboundary bristles is;therefore, commuously met with.

In brushes having bristles of varying diameters, 1

the amount of deflection of any bristledepends upon the averageresisting" force "of adjacent bristles, and it frequently happens thatthe average deflection producedupon the large and small d ameterbristles alike is in excess of the deflection which the largediameter'bristles are able to stand? repeatedly, with the resultthat'the large diameter bristles fail after a comparatively fewflexures. I

In the case of bristles along the trailing edge of the brush, both largeand small diameter bristles are frequently deflected to. an extent"greater than'the average deflection of the bristles in'the brushgenerally; due to the fact that the outer trailing rowof bristleslacksthesupport afforded by adjacent rows. fBristle breakage due'to thefatigue stresses developed by repeated fiexures therefore frequentlyoccurs to a greater extent along I the outer rows of l a brush thanelsewhere in the brush. 1 l 1 We have discovered that fatigue failureofbris tles'can be reducedto: a considerable extent by providingasupportingsurface adjacent the outer bristles of a bristle tuft, whichsurfaceis 'designed so as to lend support to such bristles when stresseswithin the bristle material approach the endurance limit. i f 1 It istherefore an object of the invention'to provide a brush construction inwhich the bristlesaresupported so as so that the life'of the bristles ofthe brush may be extended in service. i i i It, is a further object toprovide a brushlconstruction in which the torelieve fatigue stressesbristle-supporting surface comprises a"rid"ge adjacent the outer rows oftufts of a brush which is shaped so as tos'upport said outer bristles,and in which the. bristlereceiving apertures are also shaped inaccordance with such surface shape so as to relieve stress concentrationin the bristles elsewhere thebrush.

It is alsoan'objectof the invention toprovide a construction in whichstrains are reduced and distributed in those sections of the bristles.adjacent the brush head, whereby the phenomenon within commonly known asnotching of the bristles r with respect to tooth brush and breakage ofthe bristles is reduced.

It is a further object of the invention to provide amethod for formingthebristle supporting surface and bristle-receiving apertures'so as'toconform with a predetermined surface curvature, whereby undue stressconcentration in the bristlesflmay be eliminated. I

It is also an object of the invention to provide a construction whichmay be easily cleaned. is applicable generally to brush construction,for example .to clothes brushes, fto'oth brushes, scrubbing brushes,brooms, rotary brushes, and others, ari'd'it is The present, inventlontherefore an objectof the invention to apply v the constructiontosuchbrushesg v i The principlespf this invention are illustratedconstruction but this is not to beunderstood as limiting the scope ofthe invention.

In the description hereinafter given, reference is had to theaccompanying drawings in which like characters represent correspondingparts in all views. V l Figure 1 is a plan View of a brush handle withthe bristles removed;- I a Figure 2 is an elevation partly in sectionshowing some of the bristles in place and some removed. 1 a 3 Figure 3is a sectionalview along the lines 3-3 ofFigure 2. 4 g t Figure 4 is afragmentary enlargement in section of the bristle receiving opening-ofthe brush, shown in-Figure 3. I i 1 Figure 5 isian enlarged view of onebristle and the bristle-supporting surface, showingthe derivation of thesurface shape.

Figure 6 is an enlarged section of a modificationof the presentinvention.

Figure '7 is a fragmentary enlargement in sec-f fication shown in Figure-6.

Figure 8 is a fragmentary enlargement of the i selected for thebristle-receiving aperture of another modification of the invention.

Figure 9 is a fragmentary plan View of the bristle-receiving aperture ofthe brush modification illustrated in Figure 8.

In the construction illustrated in Figures 1 through 4 the brushconsists of a head portion l and a handle 2 bywhich the brush ismanipulated. The head 1 is elongated and is provided with a plurality ofbristle-receiving apertures 3 which in this particular construction arear- Each aperture ranged in two longitudinal rows. supports a bristletuft 4 consisting of a plurality of individual bristles bent over staple5 as shown in Figure 3.

6 of curved cross-section which serves as a support for the bristles oftufts 4 when the bristles are, deflected. In the construction shown inFigures 1 through 4, apertures 3 intersect ridge 6, although this is notan essential feature of the invention, as hereinafter pointed out.

The shape of the bristle-supporting surface 8 of'th'e'aperture 'andofthat portion of the ridge 6 which is adjacent the aperture may bedetermined empirically or it may be derived mathematically. The numeral8 in this application is used'to denote both'the bristle-supportingsurface and the bristle deflection curve from which the surface shape isderived, as hereinafter pointed out. Y

. According to'the empirical method, a flexible bristle A is supportedvertically, as shown in Figure 5, and then deflected by a force Fapplied at rightangles to the axis of the bristle until the bristle isdeflected to the extent'commonly met within practice, which in the caseof a tooth brush, is when a line drawn through the tip -T and base B'ofthe bristle, is in the neighborhood of forty-five degrees. Thisangularity, of course, depends upon the brush and the service to whichit is subjected. Itis to be understood that the average bristles of thebrush are stressed to about the endurance limit when deflected to thisamount, and the supporting ridge is intended to be operative to lendsupport to the bristles if deflected beyond the 45 degree limit and tolend support to large bristles which are not average and which arestressed beyond the endurance limit when deflected to the forty-fivedegree limit. It is also 0 be understood that the bristle experimentaldetermination is sufficiently thin and flexible that it will not bestressed beyond the elastic limit during test, that is tov say, itreturns to a substantially upright position when released. The curve 8of the deflected bristle is then determined photographically or bydirect measurement and this curve is reproduced as thebristle-supporting surface 8 of the ridge 6. .The portions l of' theridge between the bristle-receiving apertures donot ordinarily act as abristle-supporting surface and hence may be of any desiredcross-section, but are for convenience made of the same curvature as theportions of the ridge which are adjacent the apertures.

The mathematic method of determining the curve 8 of ridge 6 is basedupon the following formula:

ex 3X iw 7 L Adjacent each of the rows isa ridge.

, analysis.

and depends upon the deflection to which the bristle is subjected. Theseapplied in Figure 5.

It has been found that a portion of the curve expressed by the aboveequation may be approxvarious symbols are imated by a segment of acircle, the diameter and center of which'maybe determined either byknown methods of graphic or mathematical Thus, when the bristle length Sis 1i inch, the factor L has a value of .305 and the circle whichapproximates the curve mathematically expressed above, has a radius ofinch about a center which is slightly above the face of thebrush head.The bristle-supporting surface'B, therefore, may be formed to thisdimen- S1011.

The height of the ridge may be obtained from the following expression:H=LXK+C where H equals the height in inches of the ridge, L is asabovedefined. The factor X is applicable in a construction such as thatshown in Figures 8 and 9, and. equals the value of X in the previouslystated equation when Y equals -K, and K equals the extreme variation ortolerance in position of the bristle-receiving aperture with referenceto the ridge. The factor C in this expression is a constant whichdepends upon a number of considerations, including the following:

(a) The support gained in case of excessive deformation.

(b) The position of the center of the bristlereceiving aperturewithreference to the curved surface.

(c). The effect of the height upon the sanitary features of the brush.

(d) The height required to prevent the spreading of the bristles of thetuft and the subsequent application of excessive forces or extremepressures on a few remaining bristles in the tuft.

(e) The effect of the height upon the appearance of the brush.

Referring nowto Figure 4 it will be seen how the bristle deflectioncurve8 is utilized in forming the bristle-receiving aperture and to thatportion of the ridge 6 which is adjacent the aperture. The lower part ofthe aperture 3 from levelsHi to H2 is of circular cylindricalcross-section. From the leverI-Iz to Hz, the inner surface 8 of theaperture is a surface of revolution of the curve '8 about the centerline of the aperture. Above level H3 and to the right of line la thereis a portion 9 which forms the smoothly rounded entrance to the aperturefrom the surface ll of back I. To the left of line 1 and above level Ha,area 10 is a continuation of the surface of revolution of curve 8 wherethat surface intersects ridge'6.

The bristles'within the aperture are thus completely supported in everydirection by the surface of revolution of curve 8 as high as level H3and are additionally supported to level H5 by a continuation of thissurface on the ridge side.

= It should beunderstood that the support given to outermost bristles of-thetufts; are transmitted to adjacent bristles within the tuft, thusprotecting them against harmful deflection.

The brush back I and surfaces8, 9 and ID are preferably formed bymolding, such as by injecting a hot viscous material intoa mold,'or byhot holding a'heat hardenable resinous material. Another method offorming the surface is by hot pressing a pre-cut blank of'Celluloid orother material capable of flowing under pressure at elevatedtemperatures. If desired the bristle-receiving apertures maybe-molded orpressed to form, for instance, surfaces 8, 9 and I0, and then drilled soas to form the circular cylindrical portion of the aperture. The "moldedor hot pressed blank' with its completely formed surfaces 8, 9 and It]thus serves to assist-accurate drilling.

Figures 6 and 7 showamodification of the invention in which backli'sprovided with upstanding ridges l3 which-support the bristles. In thismodification theridge [3 has an inner surface l4 which is parallel tothe axis l 2 offthe tuft. When the tufts of the brush shown in Fig ure 6are deflected beyond'th'e average endurance limit of the bristles,thejoutermost bristles are supported at the points I5 I and [6, theridge height being such that these support points lie along thedeflection curve 8 of a perfectly flexible bristle. These points,therefore, serve to distribute the deflection over a considerable lengthof the bristle and thus preventthe bristle from being deformed beyondits endurance limit at any point. It should be understood that thesupport given to any outermost bristle is transmitted to adjacentbristles, thus protecting them also from 2 undue deflection. v H ,7

The bristle-receiving apertures 3 of the brush, shown in Figure 6, ispreferably formed, as shown in Figure 7, with a curved entrance similarto that shown to the right of the line Tin Figure 4, that is, with asection 8 between level Hz and H3 which is a surface of revolution ofthe bristle deflection curve 8 about centerline l2, and with a smoothlycurved entrance section 9, between levels H3. and H4, joining with theaforesaid surface of revolution.

The modification shown in Figures 6 and '7 has the especialadvantiagethat the bristle-receiving aperture can be formed byarevolving tool since the aperture shape does not intersect the adjacentridge. Thus the holes can be drilled and then reamed with a cuttershaped to give the desired curvature to the aperture entrance. Ofcourse, this form can also be obtained by molding orhot pressing ifdesiredyas with the form shown in Figures 1 through 4. v

A third modification of the invention is illustrated in Figures 8 and 9.In this form of the invention the bristle-receiving aperture is acircular cylinder from level H1 to level H2, and the same cylindricalshape is continued above level H3, to the left of vertical line 22 (seeFigure 8). To the right of line 22, the aperture is shaped with surfaces8 and 9, the same as for the corresponding surfaces of the modificationshown in Figure 4. The ridge in this modification has a cross-sectionalcurve which conforms with the bristle deflection curve 8 ofa perfectlyflexible bristle, derived as shown in Figure 5, and the intersectionportion 23 is smoothly rounded so as to prevent undue stressconcentration of a bristle bent over the intersection line.

It is recognized that in this modification, a defiected bristle in theposition 24 of Figure 9 would be deflected about a shorter radius ofcurvature than at any place in Figure 8, but this is accepted as adesign'compromise in order that a considerable number of bristles inareas 25-45 may receive the full benefits of the ridge curvature.

The advantage of the construction shownin Figure 8 is that the bristleapertures may be drilled. The curved off intersection as "between levelsHz and H4, and at 23 may be 'formed'bymolding or by any other desiredprocess.

The dimension Kisthe tolerance permitted in the position of aperture 3with respect to ridge 6 and is a factor (k) in the ridge height H=LXK+C.Thus in the'brush specifically illustrated in Figures '7' and 8, whenthe tolerance factor K equals .0096, C is .02 inch, and the bristlelength is inch, the height'H of the ridge 6 Wi1lbe.065inch." 'Ifdesired, bristle-supporting ridges of any of the brushes may haveinwardly curved ends which partially enclose the end tufts of each rowand thus lend-endwise supportto the endwise bristles of th'eend tufts,This is illustrated in the form of brush shown in Figures 1 through 4 inwhich the ridges 6 are curved in'wardly at l8 and shaped so as tosupport the outermost bristles of the end tufts. The inner curved endsl8 do not join each other and they therefore provide free passageways l9and 2ll at each end of the brush, for the flow of liquid during cleaningof the brush, thereby preventing an accumulation of debris andtoothpaste which might otherwise render the brush unserviceable. It hasbeen found that the side ridges along the brush have the effect ofconcentrating thewater flow along the brush, thus assisting the cleaningaction. In all modifications of the invention, the junction between theridge and'the brush back is smoothlyfilleted to prevent. the lodging ofdebris, etc., thefillet curve being illustrated at 2| in Figures4,6,7and8. n d w I It frequently happe s that brushes such as thetoothbrushes illustrated contain bristles of varyingdiameters. If abristleis of small diameter, or is freely elastic, deflection to, forinstance the position of the curve 8 in Figures 3, 4, 5 and '7 wouldsimply causethe bristle to assume a free position following the curve.However, when a stiffer bristle,,or one of larger diameter is similarlydeflected itwould be excessively strained, or deformed, except that thebristle is forced to curve over. the ridge, vrl'iich accordinglydistributes the stress and saves the bristle from concentr'ated stressand consequent breakage. The protective ridge of the brush, therefore,enables the brush to be used for a longer time than those made accordingto previous methods.

A tooth brush designed according to the present invention has hadexcellent lasting qualities even though the brush had only two rows ofsix tufts each, and even though mixed bundles of bristles of diametersfrom to inch were used.

We claim as our invention:

1. A bristle brush comprising a head, bristles mounted on said head toproject from a face thereof, and means for supporting the outer of saidbristles against outward deflection comprising a supporting ridge havinga curved bristlesupporting surface rising from the plane of said faceand from adjacent the outer sides of said outer bristles at said plane,said bristle-supporting surface being continuously curved away from thenormal unflexed position of said bristles from said plane tosubstantially the top of the ridge, whereby said outer bristles willengage said supporting surface at. polntszpr'ogressively farther removedfrom th'eir normal unflexed positions, along their lengths from the saidplane tothe top of the ridge, when said bristles are deflected in thedirection of said supporting surface.

2. A tooth brush, comprising a head, a plurality of rows of bristlesmounted on said head to project from a face thereof, ridges rising abovesaid supporting surface at points progressively father removed fromtheir normal unflexed positions, along their lengths from said plane tothe top of the ridge, when said bristles are deflected in the directionof said supporting surface.

3. A bristle brush. comprising a substantially solid brush head, ashaped longitudinal ridge of curved cross-section along the head, saidbrush h'ead having a plurality of bristle-supporting sockets thereinextending partially into said ridge at one side thereof, and a tuft ofbristles in each of said sockets.

4. A'tooth brush having, a head, a plurality of rows of bristlesprojecting from said head, bristlesupporting ridges rising from theplane of said head and paralleling the outer rows adjacent the outersides thereof, and each provided with inwardly directed portions at therow ends, said ridges being spaced at one end of the head, and saidspace being substantially free and unobstructed to provide a freedrainspace-for liquid during cleaning of the brush.

5. A tooth brush comprising a brush back, a plurality of rows of bristletufts mounted in sockets in said back,- bristle-supporting ridgesadjacent the outer rows shaped soas to provide a smoothly curved surfacefor the support of the bristles when the bristlesare deflected, theentrance of each bristle socket being smoothly curved so as to preventnotching of the bristles, said bristle-supporting surfaces of the ridgesbeing curved away from the bristles from the plane of the brush backsurface in which the bristles are mounted to substantially the top ofthe ridge.

6. A tooth brush having a head, a plurality of rows of bristles mountedon saidhead to .pro-

ject from a face thereof, ridges rising above said face and parallelingthe outer rows adjacent the outer sides thereof, and each provided withinwardly directed portions at the row ends, said ridges being spaced atone end of the head and said space being substantially free andunobstructed to provide a free drain space for liquid during cleaning ofthe brush, and said ridges each having a curved bristle-supportingsurface rising from the plane of said face and from adjacent the outerand end bristles of one of said rows at said plane, saidbristle-supporting surface being continuously curved away from thenormal unflexed position of said outer and end bristles r from saidplane to substantially the top of the ridge, whereby said outer and endbristles will engage said supporting surface at points progressivelyfarther removed from their normal unflexed positions, along theirlengths from said plane to the top of the ridge, when said bristles aredeflected in the direction of said supporting surface.

7. A bristle brush comprising a head having a ristle-receiving aperturetherein, a bristle-supporting member having a bristle-supporting surfaceadjacent to and intersected by said aperture, and a bristle knot or tuftin said aperture, the entrance curvature of the aperture and the saidbristle-supporting surfac comprising a shaped surface which is curved inaccordance with the curvature of a bristle used in the brush, whendeflected.

8. A bristle brush comprising a head having a bristle-receiving aperturetherein adjacent one edge thereof, a bristle tuft in said aperture, anda raised support between said tuft and said edge of the head, saidsupport having a bristle-supporting surface facing said tuft, whichsurface lies closely adjacent said tuft where the latter emerges fromsaid aperture and curves away from said tuft, substantially continuouslyfrom said head to the top of the ridge.

9. A tooth brush comprising a head, raised bristle-supporting meansalong each longitudinal edge of the head, bristles mounted on said headintermediate of said supporting means and normally substantially out ofcontact with said supporting means, said supporting means being adaptedto support the outer bristles when outwardly flexed and being laterallyspaced at one end of the head to facilitate ready flushing of the brush,the said lateral space being free and unobstructed.

GLEN E. MILLARD. WILLIAM G. HUGHES.

